An example of an internal combustion engine having connecting rod-to-pin connections is shown in FIG. 1. The engine in FIG. 1 is an opposed-piston, opposed-cylinder (OPOC) engine 10 of the type described in U.S. Pat. Nos. 6,170,443, and 7,434,550, which are incorporated herein by reference.
In the left cylinder (cylinders not shown in FIG. 1) are outer piston 12 and inner piston 14. Outer piston 12 is coupled to crankshaft 20 via two pullrods 18 at a big end of pullrods 18. Pullrods 18 couple to a bridge 22 on a small end of pullrods 18. Inner piston 14 is coupled to crankshaft 20 by a pushrod 16. Pistons 12′ and 14′ in the right cylinder (not shown) are coupled to crankshaft 20 by pushrod 16 and pullrods 18, respectively. The crankshaft has two main bearings 26, a centrally-located journal bearing (not shown) to which pushrods 16 are coupled, and two offset journals, each one of which has two pullrods 18 coupled thereto.
Bridge 22 reciprocates along the Y axis with virtually no motion in the Z direction. In contrast, the big end 28 of pullrods 18 moves in the Z direction in response to the rotation of crankshaft 20. By virtue of motion of the big end 28 of pullrods 18 in the Z direction, pullrods 18 rock in relation to bridge 22. There is relative motion between a cylindrical pin 23 that extends from bridge 22 and the pullrod 18 into which pin 23 extends. Commonly, a bearing 24 is provided between the inner surface of pullrod 18 and pin 23. Bearing 24 can be a sleeve bearing or needle bearings.
During operation in a two-stroke OPOC, pullrods 18 are almost always in tension and pushrods 16 are almost always in compression. When bearings 24 are sleeve bearings, one side of the sleeve bearing is squeezed between pullrod 18 and pin 23 such that lubricant is squeezed out. Relative movement between the connecting rod and the pin can lead to wear of the bearing surfaces due to a lack of lubrication. Alternatively, bearings 24 are needle bearings. Needle bearings have issues of providing sufficient contact area. Furthermore, there are applications in which needle bearings are not suitable. It is desirable to have a joint between the connecting rod and the pin that depends less on lubrication and is substantially frictionless.